• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.126-128
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• 2001

In this paper, Magnetic Flux Leakage(MFL) method is used to detect surface defect in ferromagnetic plate. Surface defects are created on the SM 45C ferromagnetic plate and magnetizing equipment is composed to perform MFL nondestructive testing. The length and width of defect is twice the thickness of ferromagnetic plate, and defects with different depths are made artificially for the experiment. Also, NdFeB magnet in magnetizing equipment is used to make magnetic flux. This paper shows that it is possibile to detect 10% defect and to analyze numerically for any defect using MFL method.

• Carbon letters
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• v.13 no.1
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• pp.56-59
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• 2012

The defect sites on chemical vapor deposition grown graphene are investigated through the selective electrochemical deposition (SED) of Au nanoparticles. For SED of Au nanoparticles, an engineered potential pulse is applied to the working electrode versus the reference electrode, thereby highlighting the defect sites, which are more reactive relative to the pristine surface. Most defect sites decorated by Au nanoparticles are situated along the Cu grain boundaries, implying that the origin of the defects lies in the synthesis of uneven graphene layers on the rough Cu surface.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.637-642
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• 2011

Rails are subjected to damage from rolling contact fatigue, which leads to defects such as cracks. Rolling contact fatigue damages on the surface of rail such as head check, squats are one of growing problems. Another form of rail surface damage, known as "Ballast imprint" has become apparent. This form of damage is associated with ballast particles becoming trapped between the wheel and the surface of rail. These defects are still one of the key reasons for rail maintenance and replacement. In this study, we have investigated whether the ballast imprint is an initiator of head check type cracks and effect of defect size using Finite element analysis. The FE analysis were used to investigate stresses and strains in subsurface of defects according to variation of defect size. Based on loading cycles obtained from FE analysis, fatigue analysis for each point was carried out.

• Journal of the Korean Society for Nondestructive Testing
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• v.6 no.1
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• pp.23-30
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• 1986

The optimumultrasonic test conditions for the thin carbon fiber reinforced plastic (CFRP) sheet were determined for the immersed reflector plate method. The effects of the water distance, the surface conditions of the specimen and transducer characteristics were studied. For a reliable test the water distance between the transducer and the front surface of the specimen should be determined when the beam profile of the transducer appears in the bell-shape. The detectability of the defect was improved as the effective beam width of the ultrasonic transducer became narrow. The transducer should be properly chosen considering to the surface condition of the test material as well as the size and type of the defect to be detected. It was possible to detect the flat bottom hole whose diameter is as small as about 500 micrometer.

• Journal of Power System Engineering
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• v.8 no.3
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• pp.52-57
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• 2004

A new non-destructive inspection technique has been developed. One characteristic of the technique is that defects are visualized by laser ray. Magnetic domains and domain walls of a magneto-optical sensor(MO sensor) are varied by the magnetic flux leaked by defects, and the variations are observed by the reflected light of the laser ray. The information of defect can remotely be inspected by this technique in a real time. This paper describes the results estimated on the 2-dimensional surface defects and opposite-side defects in a ferromagnetic material and the natural surface defect in a clutch disk wheel. The light region of a visible image and the magnitude of a reflected light increases as the input current of the magnetizer increases. The natural surface defect, that has not the width of crack's open mouth, can be also visualized like as 2-dimensional artificial defects.

• Journal of Welding and Joining
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• v.16 no.6
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• pp.77-85
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• 1998

Effects of non-cleaning and cleaning fluxes on the wetting properties and defects at flow soldered joints were investigated. Non-cleaning flux (R-type of 3.3% solid content) and cleaning flux (RMA-type of 15% solid content) were used. Wetting test was accomplished by wetting balance method with changing surface state of wetting specimen, CU. Sn-37%Pb solder was used for wetting test and flow soldering. As experimental results, the wetting time for vertical force from the surface tension being zero was mainly affected by surface state of the wetting specimen. Non-cleaning flux had a good wettability compared with cleaning flux. In case of non-cleaning flux, conveyor speed had a great affection to defects of bridge, icicle, and poor solder.

• Journal of the Korean Society of Safety
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• v.14 no.3
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• pp.25-32
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• 1999

This study has been performed to investigate the stress distribution around defects that behave as stress concentrators. Besides, the effect of stress interaction effects on the initiation of primary cracks were also investigated by rotary bending fatigue tests which were performed with specimens drilled micro surface defects and the stress distribution was analyzed using Finite Element Method. In addition, the stress interaction effects around defects and cracks were investigated by comparing the results of experiments and F.E.M. The results obtained are summarized as follows ; 1) Area which slip and micro cracks initiated at micro surface defects is between the maximum shear stress points and this area is over than ${\pm}30^{\circ}$ from the maximum stress point along the defect edge. 2) The stress interaction effect for the small size defect is larger than that of large size defect when the interval between them is near 3) Interval which there is no shear stress interaction effect analyzed by F.E.M. is larger than that of experimental results.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.137-139
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• 2007

In optical disk drives, a conventional control method in the presence of surface defect is holding the previous tracking control command. It is known that the method has a long settling time. This paper proposes a new control method which reduces the settling time. An optical head generally has coupled dynamics between focusing and tracking servo system. We present how to compensate the coupled dynamics so that reduced settling time is achieved. It is verified by experiments that the proposed method brings an improved performance in the presence of surface defect as well as in the normal operating condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.11a
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• pp.54-58
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• 1994

H$_2$ bake and GeH$_4$ clean are used as a in-situ pre-clean method in low temperature Si based epitaxial growth technology using rapid thermal processing chemical vapor deposition (RTPCVD). In this paper, the H$_2$ bake and GeH$_4$ clean processes are optimized for low surface defect density using Taguchi method. In H$_2$ bake process, the epitaxial growth temperature affects dominantly on the surface defect density, and the next affecting factors are H$_2$ bake temperature and rinse time in de-ionised water. In GeH$_4$ clean process, GeH$_4$ clean temperature affects most strongly on the surface defect density, and the minor factor is GeH$_4$flow rate. The optimum process conditions predicted fly Taguchi method agree well with tile experimental data in both in-situ clean processes.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.8 s.185
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• pp.80-88
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• 2006

This paper proposes a new steel strip surface inspection system. The system acquires bright and dark field images of defects by using a stroboscopic IR LED illuminator and area camera system and the defect images are preprocessed and segmented in real time for feature extraction. 4113 defect samples of hot rolled steel strip are used to develop KNN (k- Nearest Neighbor) classifier which classifies the defects into 8 different types. The developed KNN classifier demonstrates about 85% classifying performance which is considered very plausible result.